U.S. patent application number 17/272667 was filed with the patent office on 2021-11-04 for spectrograph recycling.
The applicant listed for this patent is Michigan Aerospace Corporation. Invention is credited to Will JOHNSON.
Application Number | 20210341334 17/272667 |
Document ID | / |
Family ID | 1000005740947 |
Filed Date | 2021-11-04 |
United States Patent
Application |
20210341334 |
Kind Code |
A1 |
JOHNSON; Will |
November 4, 2021 |
SPECTROGRAPH RECYCLING
Abstract
Spectrographic measurements are often limited by the amount of
light that is available. Photons that are not collected or measured
reduce the signal to noise and therefore reduce measurement
precision. This invention collects the zero order light and sends
it through the spectrometer again. In an atmospheric LIDAR, the
zero order recycling is estimated to increase the rotational Raman
signal by an additional 20%. A grating based spectrometer where the
zero order light is collected by a lens or mirror and focused into
a fiber optic that sends the light to the input slit where it is
directed into the spectrometer again. There can be a plurality of
recycle fibers. The detector can be either a single linear array or
a two dimensional array such as a CCD or CMOS camera.
Inventors: |
JOHNSON; Will; (Saline,
MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Michigan Aerospace Corporation |
Ann Arbor |
MI |
US |
|
|
Family ID: |
1000005740947 |
Appl. No.: |
17/272667 |
Filed: |
September 4, 2019 |
PCT Filed: |
September 4, 2019 |
PCT NO: |
PCT/US19/49461 |
371 Date: |
March 2, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62726561 |
Sep 4, 2018 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01S 17/95 20130101;
G01J 2003/2813 20130101; G01J 3/0221 20130101; G02B 6/0008
20130101; G01J 3/18 20130101; G01J 3/2803 20130101 |
International
Class: |
G01J 3/02 20060101
G01J003/02; F21V 8/00 20060101 F21V008/00; G01J 3/18 20060101
G01J003/18; G01J 3/28 20060101 G01J003/28; G01S 17/95 20060101
G01S017/95 |
Claims
1. A grating based spectrometer, comprising: an input optic fiber;
a recycling optic fiber; a grating; a first focusing mirror; a
detector; and a collimating mirror positioned to collimate light
from the input optic fiber and direct the light to the grating,
wherein a portion of the light striking the grating is reflected
into at least a zero order, the light diffracted by the grating is
captured by the first focusing mirror, first and second diffracted
light from the grating are collected by the first focusing mirror
and focused on the detector, and the zero order light is collected
and focused into recycling optic fiber that sends the zero order
light back to the collimating mirror so as to be directed again
into the spectrometer.
2. A grating based spectrometer according to claim 1, further
comprising: a plurality of recycling optic fibers.
3. A grating based spectrometer according to claim 1, wherein the
detector is at least one of a single linear array and a two
dimensional array.
4. A grating based spectrometer according to claim 3, wherein the
detector is at least one of a CCD and CMOS camera.
5. A grating based spectrometer according to claim 1, further
comprising: A focusing element operatively positioned to collect
and focus the zero order light into the recycling optic fiber.
6. A grating based spectrometer according to claim 3, wherein the
focusing element is at least one of a lens and second focusing
mirror.
Description
I. BACKGROUND OF INVENTION
A. Scope of the Invention
[0001] This invention uses or recycles the zero order light from a
diffraction grating based spectrograph. Estimates of the
improvement made in the performance of a spectrograph so configured
indicate that the output signal could be increased by 20
percent.
B. Summary of the Prior Art
[0002] Spectrographic measurements are often limited by the amount
of light that is available. Photons that are not collected or
measured reduce the signal to noise, and therefore reduce
measurement precision. In current spectrographs, the zero order
light is not used even though it is a significant portion of the
incoming light. Typically, the zero order light is absorbed to
reduce the potential for the zero order light scattering and
contaminating the diffracted light that one wishes to measure.
II. SUMMARY OF THE INVENTION
[0003] Spectrographic measurements are often limited by the amount
of light that is available. Photons that are not collected or
measured reduce the signal to noise and therefore reduce
measurement precision. This invention collects the zero order light
and sends it through the spectrometer again. In an atmospheric
LIDAR, the zero order recycling is estimated to increase the
rotational Raman signal by an additional 20%. The present invention
is directed to providing and implementing a grating-based
spectrometer where the zero order light is collected by a lens or
mirror and focused into a fiber optic that sends the light to the
input slit where it is re-directed back into the spectrometer.
III. BRIEF DESCRIPTION OF THE DRAWINGS
[0004] The present invention is illustrated in the accompanying
drawings, wherein: FIG. 1 illustrates a diffraction grating
spectrometer that shows the zero order light that is not usually
shown as known in the prior art;
[0005] FIG. 2 shows a lens capturing the zero order and coupling
the light into an optical fiber according to the present
invention;
[0006] FIG. 3A shows the arrangement of the input fiber and the
spectrometer slit according to the present invention;
[0007] FIG. 3B shows the arrangement of the input and recycle fiber
and the spectrometer slit according to the present invention;
[0008] FIG. 4A shows the fiber image on a portion of the detector
array for the input light according to the present invention;
and
[0009] FIG. 4B shows the fiber image of the input and recycle fiber
on a portion of the detector array for two wavelengths of light
according to the present invention.
IV. DESCRIPTION OF THE PREFERRED EMBODIMENT
[0010] The embodiments of the present invention will be described
hereinbelow in conjunction with the above-described drawings. FIG.
1 shows a prior art spectrograph system that uses reflective optics
and diffraction grating. In the general operation of the system,
light is input to the spectrometer 100 via a fiber optic 10 through
a slit 20 and onto a first mirror 21. The first mirror 21
collimates the light from the fiber 10 and directs the light to the
grating 22. Light that strikes the grating is reflected into the
zero order 12 as well as the order to which the grating is designed
to reflect the maximum energy for a given wavelength.
[0011] The light diffracted by the grating 22 is captured by a
focusing mirror 23 and an image of the input fiber for a wavelength
is reconstructed on the detectors 25. The diffracted light 13 and
14 for the first wavelength 13 and second wavelength 14 is
collected by the focusing mirror 23 and focused on the detector
array 25. In FIG. 1, the light from the zero order is shown going
off into space. In the prior art designs, that light is lost.
[0012] In a spectrometer 200 according to the present invention, as
shown in FIG. 2, the zero order light is captured by a focusing
element 24, in this embodiment a lens, that focuses the zero order
light 12 into the recycle fiber optic 30 that then re-directs the
captured zero order light back to the input slit 20 of the
spectrometer 200. In another embodiment, the focusing element 24
may be implemented as a mirror (not shown), a combination thereof,
or any other device known in the art having similar functionality
to capture and focus the zero order light.
[0013] FIG. 3A shows the relationship between the input fiber 10
and the slit 20 according to the prior art. FIG. 3B shows how the
recycle fiber 30 is arranged below the input fiber 10 and relative
to the slit 20 according to the present invention. Although this
embodiment illustrates the input fiber 10 above the recycle fiber
30, the order could be switched without impacting the operation of
the system.
[0014] FIG. 4A shows how the diffracted light at a first wavelength
13 and at a second wavelength 14 are imaged on the elements 40 of
the detector array 25 (see FIG. 2). In at least one embodiment, the
detector array 25 may be implemented as a single linear
photodetector array or a two-dimensional array such as a CCD or
CMOS camera. The image of the first wavelength 51 and the image of
the second wavelength 52 are shown on the detector elements 40. In
practice, the images 51 and 52 may be larger or smaller that the
examples used in the drawings. FIG. 4B shows how the recycled zero
order light 12 is focused on the detector elements 40. The image of
the first wavelength 51 and the image of the second wavelength 52
are shown along with a first wavelength recycle image 53 and a
second wavelength recycle image 54.
[0015] The detector elements 40 are shown to be rectangular in this
embodiment, but could be square, circular or any other arrangement
known in the art. In this embodiment, the detector array 25 is
implemented as an array of photomultipliers that have a rectangular
active area. Other geometries for a detector array or other
photodetectors with similar functionalities as known in the art
could also be used.
[0016] It should be noted that, in the examples illustrated in
FIGS. 4A and 4B, the images of the first wavelength 51 and second
wavelength 52 are shown as circles that are aligned with the
detector elements 40. That is not a necessary requirement and in
actual practice, the images will be spread over multiple detector
elements 40.
[0017] While the preferred embodiment uses a single recycle, there
may be cases where additional recycle fibers could be added to the
system to gain additional signal. As such, the recycle fiber optic
30 may be implemented as a single recycle fiber, a plurality of
recycle fibers, or any other device known in the art having similar
functionality transmit the zero order light from the focusing
element 24 back to the input slit 20. The limiting factor in the
number of recycle fibers is the height of the input slit 20. Each
recycle fiber occupies a portion of the slit 20 and the recycle
fibers could over fill the slit with the result of overfilling the
slit and causing a loss in inputted light energy.
[0018] Although the present invention has been fully described in
connection with the preferred embodiment thereof with reference to
the accompanying drawings, it is to be noted that various changes
and modifications will be apparent to those skilled in the art.
Such changes and modifications are to be understood as included
within the scope of the present invention as defined by the
appended claims, unless they depart therefrom.
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